Control method of tension in rolling mills (2)

ABSTRACT

In a cold tandem mill of the endless type, the tension of the strip is maintained constant during the transitional period that the cross section of the strip undergoes a change in size as the thickness, the width or the finished thickness of the strip is being changed.

United States Patent 1 1 ROLLING LOAD F} m 8 r 6 DAMPING DEVICE I6 ARITHMETIC CIRCUIT TENSION T Fujii et al. Oct. 23, 1973 CONTROL METHOD OF TENSION 1N 3,015,974 1/1962 Orbomet aI .[72 9 ROLLING MILLS (2) 3,332,263 7/1967 A 3,618,348 Il/1971 Arlmura et al. 72/7 [75 Inventors: Seiji Fujii; HiroshI Kuwamoto; 3,281,917 11/1966 Teplitz 29/33 Masamoto Kamata; Masayuki lshida, all of Fukuyama, Japan I z K Kabush-ki ha Primary Examiner-Milton S. Mehr Asslggee lppon an 1 Is k Att0rney-Robert D. Flynn et al.

[22] Filed: Aug. 24, 1971 I [21] Appl. No.: 174,485

- 57 ABSTRACT [30] Foreign Application Priority Data 1 Aug. 29,1970 Japan 45/75440 In a cold tandem mill of the endless yp the tension of the strip is maintained constant during the transifi i 3 tional period that the cross section of the strip under- 'f l0 72 goes a change in size as the thickness, the width or the [I 1e 0 earc finished thickness of the Strip is being changed 5 6] References Cited UNITED STATES PATENTS 9 Claims, 1 Drawing Figure 3,603,124 9/1971 Armura et al. 72/8 MEMORY ClRbulT S-t-P/M ROLL POSITION SIGNAL S '3 f i DEVICE TENSION CONTROL CIRCUIT CONTROL METHOD OF TENSION IN ROLLING MILLS (2) BACKGROUND OF THE INVENTION In a large scale cold tandem mills, it is the recent trend that bigger and longer coils are used and further, that the material strips supplied to the rolls are welded preliminary so that the strips will be in an endless form. Under the circumstances, it has become necessary to conduct a speedy and automatic control of the strip tension between the stands of such a cold tandem roll train so that products of different shapes may be obtained from one endless rolling operation.

The present invention concerns a control method of maintaining a constant tension per unit cross sectional area during the rolling process even when the plate thickness is changed during rolling of strips.

As the art of changing the strip thickness during rolling is an entirely new art, there is naturally no prior method of control for this operation. However, there has been up to now methods such as detecting the total strip tension with a tension meter, and controlling the roll gaps or the roll speed in'the preceding and succeeding stands to maintain the total tension constant. However, the tension measured by the tension meter is the total tension of the whole length of the strip, whereas the desired value to be controlled during rolling is the tension per unti cross sectional area hereinafter referred to as tensile stress). In a batch type rolling mill where one length of strip is rolled in one operation, there is no need to change the strip thickness during rolling. Therefore, calculation of an aimed or desired value for the total tension prior to the start of the rolling operation by multiplying, the aimed (or desired) tensile stress by the thickness and the width of the plate will eliminate the need to change the value during rolling. In the endless type rolling mills wherein the thickness and/or width of the material strip or the aimed finished thickness and/or width is changed during rolling, this known control to maintain the total tension constant is not adequate, since the tensile stress will become different from the aimed value at the point that the thickness and/or width of the strip is changed.

In order to obviate such defects, it is possible to time the change of the strip thickness with the change of th aimed total tension value. However, the tension tends to become transitionally abnormal when such timing is not conducted properly.

In view of the foregoing, there has been a strong demand in the art for development of a controlmethod that will automatically change the aimed value of the total tension corresponding to the change in the strip thickness and/or. width during rolling operation.

The present invention has been contrived in view of the above mentioned situation and offers amethod of tension control of a rolling machine wherein the detected variation in strip thickness during size alteration is divided by the strip thickness prior to the size alteration, i.e., Ah/h'; and the detected width variation during size alteration is divided by the strip width prior to size variation, i.e., Aw/w; the value of 1 is added to the total of the two, i.e., 1+(Ah/h) (Aw/w) and the value thus obtained is multiplied by the values of the total tension prior to the size alteration, i.e., T,,[ 1+(Ah/h) (Aw/w)]. This value thus obtained is set as an aimed value of the total tension to the tension control in accordance with the present invention.

The total tension of the strip is obtained by multiplication of the tensile stress, the strip thickness and the strip width.

AT= T[(Ah/h) (Aw/w)] T+AT= T[ 1+Ah/h (Aw/w)] The formula (3) is rewritten by maintaining the total tension desired value before the size alteration as T and the total tension desired value after the size alteration as T then the formula (4) is obtained:

Based on the formula (4), one example of the circuit for automatically altering the aimed value for the total tension in accordance with the present invention is shown in the single FIGURE of the accompanying drawing.

Referring to the single FIGURE, there is shown a tandem rolling mill having a plurality of stands and wherein the tensile stress between the (i)the stand and the (i+1)th stand are kept at an aimed value. In the diagram, (1) denotes (i)th stand rolling machine, (2) (i+l )th stand, (3) and (4) load cells for each stand, (5) and (6) screw down mechanisms for each stand, (7) and (8) electric motors for the screw downs of each stand, (9) and (10) electric motors for driving purposes for each stand, (11) the width measuring device, (12) a tension meter, (13) and (14) the electric delays that become off while the tensile stress is under a control to be kept constant, (16) and (17) devices, such as operational amplifiers, to divide the values from the load cell by the Mill constant (hereinafter referred to as a damping device), (18), (19) and (20) memory circuits, (21) an arithmeticcircuit, (22) a multiplier and (23) a tension control circuit.

The rolling load signal detected by a load cell(3) be-' comes P/M' at the clamping device (16), is added to the roll positioning signal to be fed into the memory circuit (18). In the memory circuit is' memorized the value immediately before the input electricrelay (13) becomes off by a servo motor or the like. .When the input relay (13) of the memory circuit (18) goes from on to off, the value of S+P/M immediately before and the successive'S+P/M values are compared and the differences Ah therebetween are fed into the damping device (17). Here, S denotes the screw positioning signal, P the rolling load signal, M the mill constant and h the strip thickness. The damping devices (l 6)'and (17) are chosen so that the damping ratio becomes M and h functions of actual physical quantities (l/M and l/h amplification ratio when the same is considered as the amplifier). M and h are to be preliminarily given by a manual operation. In a method as hereinbefore described, the electric signal corresponding to Ah/h is obtained on the output side of the damping device (17). The strip width signal detected by the strip width measuring device (11) is fed into the memory circuit (19) and the arithmetic circuit (21). In the memory circuit (19) is memorized the input value immediately before the input relay (14) became off from on. The arithmetic circuit (21) is designed so that l w /w is delivered from the two input signals W and W Accordingly, the output of the airthmetic circuit (21) is zero when the relay (14) is closed and becomes 1 w /w or Aw/w when it is open. W denotes the strip width value immediately before the relay (14) becomes of from on, and W is the strip width value detected at every moment of the control. The tension signal detected by the tension meter (12) is fed into the memory circuit (20). In the memory circuit (20) is memorized the input value immediately before the input electric relay (15) becomes of from on. The output of the memory circuit (20) and the total of the output of the clamping device (17) and the arithmetic circuit (21) is multipled by the multiplier (22) and delivered. This output represents the following formula:

When T is added to this output, there is obtained the following formula:

The obtained value becomes the aimed total tension during the control. The difference between the aimed total tension and the actual total tension is fed to the tension control circuit (23) as a deviation, and the control signal from the tension control circuit (23) is fed to the driving motor for the (i)th stand or to the screw down motor for (i+l )th stand to conduct the tension control of this invention.

In accordance with the present invention, when the sizes of the strip thickness, and/or the width the finished thickness is altered during the rolling operation, the unit tension of the strip may be maintained constant even during the transitional period. This will facilitate prevention of plate ruptures during rolling and the smooth operation of the system during size alteration.

What we claim is: i 1. In the cold rolling of metal strips in a multi-stand rolling mill, a method of tension control during a size alteration of the strip comprising the steps of:

dividing the detected plate thickness variation Ahduring the size alteration of strip thickness and width, and of finished thickness by the strip thickness h prior to said size alteration to obtain a value Ah/h;

dividing the detected strip width variation Aw during size alteration by the stripwidth w prior to said size alteration to obtain a value Aw/w;

adding the value of l to the total of said two values obtained;

multiplying the strip tension T prior to said size alteration by the value obtained in the preceding adding step to obtain a desired value of total tension; and

controlling the roll stands as a function of said desired value of total tension.

2. The method of claim 1 wherein the step of dividing the detected plate thickness variation by the strip thickness prior to said size alteration includes measuring the roll down position of the roll at a given stand; measuring the rolling load at said given stand; combining the roll position and rolling load measurements to generate a signal corresponding to the plate thickness variation; and then dividing said plate thickness variation signal by a value corresponding to the strip thickness prior to said size alteration.

3. The method of claim 2 wherein said combining step includes memorizing the measured value of roll position immediately prior to the size alteration; and combining the memorized roll position value, the roll position value during the size variation, and the rolling load during the size variation to develop a signal corresponding to said plate thickness variation.

4. The method of claim 1 wherein said step of dividing the strip width variation by the strip width prior to said size alteration includes memorizing the strip width immediately prior to said size alteration; an arithmetically combining said memorized strip width with the measured strip width during said size alteration to thereby develop a signal corresponding to the value of the strip width variation divided by the strip width during the size alteration.

5. The method of claim 2 wherein said step of dividing the strip width variation by the strip width prior to said size alteration includes memorizing the strip width immediately prior to said size alternation; and arithmetically combining said memorized strip width with the measured strip widthduring said size alteration to thereby develop a signal corresponding to the value of the strip width variation divided by the strip width during the size alteration.

6'. The method of claim 5 including the step of summing the signal corresponding to the thickness variation divided by the strip thickness prior to said size alteration and the signal corresponding to said width variation divided by said width prior to said size alteration.

7. The method of claim 1 wherein said adding step and said multiplying step together comprise summing the values obtained by said two dividing steps; multiplying saidjsummecl value. by said strip tension prior to said 1 size alteration; and multiplying the value obtained by next roll stand downstream of said given roll stand. 

1. In the cold rolling of metal strips in a multi-stand rolling mill, a method of tension control during a size alteration of the strip comprising the steps of: dividing the detected plate thickness variation Delta h during the size alteration of strip thickness and width, and of finished thickness by the strip thickness h prior to said size alteration to obtain a value Delta h/h; dividing the detected strip width variation Delta w during size alteration by the strip width w prior to said size alteration to obtain a value Delta w/w; adding the value of 1 to the total of said two values obtained; multiplying the strip tension To prior to said size alteration by the value obtained in the preceding adding step to obtain a desired value of total tension; and controlling the roll stands as a function of said desired value of total tension.
 2. The method of claim 1 wherein the step of dividing the detected plate thickness variation by the strip thickness prior to said size alteration includes measuring the roll down position of the roll at a given stand; measuring the rolling load at said given stand; combining the roll position and rolling load measurements to generate a signal corresponding to the plate thickness variation; and then dividing said plate thickness variation signal by a value corresponding to the strip thickness prior to said size alteration.
 3. The method of claim 2 wherein said combining step includes memorizing the measured value of roll position immediately prior to the size alteration; and combining the memorized roll position Value, the roll position value during the size variation, and the rolling load during the size variation to develop a signal corresponding to said plate thickness variation.
 4. The method of claim 1 wherein said step of dividing the strip width variation by the strip width prior to said size alteration includes memorizing the strip width immediately prior to said size alteration; and arithmetically combining said memorized strip width with the measured strip width during said size alteration to thereby develop a signal corresponding to the value of the strip width variation divided by the strip width during the size alteration.
 5. The method of claim 2 wherein said step of dividing the strip width variation by the strip width prior to said size alteration includes memorizing the strip width immediately prior to said size alternation; and arithmetically combining said memorized strip width with the measured strip width during said size alteration to thereby develop a signal corresponding to the value of the strip width variation divided by the strip width during the size alteration.
 6. The method of claim 5 including the step of summing the signal corresponding to the thickness variation divided by the strip thickness prior to said size alteration and the signal corresponding to said width variation divided by said width prior to said size alteration.
 7. The method of claim 1 wherein said adding step and said multiplying step together comprise summing the values obtained by said two dividing steps; multiplying said summed value by said strip tension prior to said size alteration; and multiplying the value obtained by the immediately preceding multiplying step by said strip tension prior to said size alteration to thereby obtain said desired value of total tension.
 8. The method of claim 1 wherein said controlling step includes combining said desired value of total tension with a measured value of tension during the size alteration to obtain a differential control value for controlling said roll stands.
 9. The method of claim 8 wherein said controlling step further includes controlling the roll speed at a given roll stand and controlling the rolling load at the next roll stand downstream of said given roll stand. 